Employee Benefits - Components of Net Periodic (Benefit) Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0
Interest cost	21	27
Expected return on plan assets, net of administration expenses	(33)	(34)
Amortization of prior-service cost	0	1
Amortization of net actuarial loss	17	13
Total net periodic (benefit) cost	5	7
U.K.
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	22	28
Expected return on plan assets, net of administration expenses	(39)	(49)
Amortization of prior-service cost	0	1
Amortization of net actuarial loss	7	7
Total net periodic (benefit) cost	(10)	(13)
Other
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	4	7
Expected return on plan assets, net of administration expenses	(8)	(10)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	3	3
Total net periodic (benefit) cost	$ (1)	$ 0